The present invention relates to a new and improved method of increasing the signal-to-noise ratio of a time-dependent scanning signal produced during a periodic scanning operation or method wherein a delineated or bounded and centered field is scanned line-by-line by means of a scanning device, there is produced a time-dependent additional or supplementary signal corresponding to the spacing of the momentary scanned location from the center of the field and possessing a momentary value r as well as a maximum value R, there further occurring successive line scanning operations in directions which in each case are changed through a predetermined angle in such a manner that as a function of the line width neighboring lines successively contact one another at the field boundary and within the field partially overlap and at the center of the field completely overlap.
In order to improve the comprehensibility of the objectives of the present invention and the solution proposed by the invention, it is necessary to explain the above-mentioned scanning operation on the basis of an example, however with the clear understanding that the above-described introductory portion of the invention is in no way intended to be limited to the described example or embodiment.
In the case of observation devices operating in the infrared region the examined or observed field is optically imaged in an image plane, and this image plane is scanned by a detector responsive to infrared light. This detector possesses a defined surface and scans a circular-shaped image field in the image plane in that it migrates along diameters of the image field. Moreover, it is to be understood that paths or tracks which successively follow one another in time differ by a predetermined angle in such a manner that at the periphery of the image field there just occurs a detection of all image points free of gaps or spaces. All of the paths or tracks radiate through the center of the image field, resulting in an overlapping of the paths. As a consequence thereof, during the course of a complete scanning of the image field one location thereof is scanned a number of times as a function of its spacing from the center of the image field, and specifically with a redundancy or frequency which is approximately proportional to the reciprocal value of the aforementioned spacing. This characteristic is extremely valuable for certain applications, for instance target tracking devices, provided that there is available a technique for optimumly evaluating, on the basis of theory of information, the multiple scanning of image locations. In this regard, there is presupposed that the detector- and amplifier noises impair the interpretation of a detector signal and not for instance the optical background of the observed or examined field.